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Are We Alone? A Look into Where Extra Terrestrials May Live

Jul 3, 2008
Ever since Man discovered that the world was, in fact, not flat and that the Earth revolved around the Sun and not the other way around they have been looking out into space and trying to discover what is really out there.

The study of the Universe has been driven by the desire to answer age old questions, one of the most prevalent being; are we alone? This question is certainly not new, and has been asked for centuries. However, with the advent of better technology and further space exploration we are coming ever closer to an answer. As more is learnt about other planets and moons we are able to give a clearer answer on whether extra-terrestrial life is likely to exist and where it may be.

The idea of life on other planets has been with us since ancient Egyptian times and ranges from realistic to the fantastic. Many ancient civilisations and religions have discussed the likelihood of life on other planets, with a large number not ruling out the possibility. Modern man certainly hasn't discounted the fact that intelligent life may exist elsewhere in the universe, and even that microbial life may have formed in our own solar system. The Phoenix lander mission to Mars is currently looking for signs of water on the planet at the time of writing. If water is found then the chance of finding life on Mars will skyrocket.

While the chance of finding intelligent life on Mars remains highly unlikely it has certainly sparked thought of where we may find intelligent life and what conditions it may have evolved in. We may even have to change what we consider life as we discover more about the solar system.

Organisms on Earth are composed from carbon, hydrogen, oxygen, nitrogen and phosphorus, Life on Earth also needs water to survive. Until recently it was assumed that all ecosystems would need sunlight to start the food chain from photosynthesis. However with the discovery of a thriving ecosystem deep under the ocean living from geothermal vents on the sea floor it has been discovered that life is able to exist in total darkness. This throws open a whole new range of environments that may be habitable that were previously discarded as being unsuitable.

It has been put forward that extra terrestrial life may be based on different elements than those found on Earth. Silicon is commonly promoted as an alternative to carbon as it has some very similar properties. Silicon is far more common through the universe than carbon, the solar system is said to be silicon-rich and carbon-poor. Despite being relatively carbon-poor, life on Earth has still evolved to be based on carbon, suggesting that it is far more suitable for sustaining life.

Given that we know that life on Earth has evolved and works it does make sense to search for Earth-like planets and moons if we are to find life. Given the unfathomably large size of the universe and the sheer number of planets and moons contained in it, it would seem foolish to say that we are alone in the universe. In fact, the laws of probability would state that it is almost certain that there is a planet out there with almost identical conditions to those found on Earth, where life has flourished. Given that life evolved to be so complex here it does not seem a large jump to assume that it has evolved elsewhere in the Universe. Finding it however, is another thing entirely.

Because of the vast distances involved in interstellar travel it is unlikely that we will ever travel to planets outside our solar system, at least certainly not for thousands, maybe millions of years. Currently most of the effort is being made into looking at whether life exists in our own solar system. There are several bodies that are thought of being capable of supporting life.

Mars is the most obvious place to look. Certainly there are signs of there being liquid water in the past and Mars has icy polar caps. Being that water is such a vital ingredient to life on Earth any solid evidence of flowing liquid water on Mars would provide a substantial step forwards to providing real evidence of alien life. It is generally accepted that any life we may find on the Red Planet will be microbial, but even in the event that we find microbes it will be a massive discovery. Confirmation of the existence of bacteria on Mars would open the door to the possibility of discovering life elsewhere in the solar system.

There is some evidence that there may be microbial life on Mars already. Methane cannot stay in the atmosphere for any longer than a few hundred years, but there is a substantial enough amount to suggest that it is being replenished from volcanic processes, or from life forms producing methane as a waste product. The discovery of a large amount of formaldehyde also points to possible microbial life on Mars. However both discoveries are open to debate, with many scientists believing that data has been misinterpreted. Mars also has no magnetic field, which leaves it open to cosmic rays.

It seems likely that the environment on Mars is too hostile to harbour complex multicellular organisms, but it may well be home for microbes and bacteria.

Another key area for finding extra-terrestrial life in the solar system is Titan, the largest moon of Saturn. Titan is larger than the planet Mercury and has a thick atmosphere containing 98.4% nitrogen. Titan and Earth are the only bodies in the solar system to have nitrogen-rich atmospheres, a similarity which makes the moon interesting for finding life. However it should be noted that Titan has no magnetic field and so is sometimes exposed to solar winds, believed to be extremely harmful for life.

Titan is often considered a possible place for life to have evolved. The current atmosphere there has drawn comparisons with the atmosphere present on early-Earth. There are lakes of liquid methane on the -290 degrees surface, and possible liquid ammonia lakes beneath the surface of Titan. These have been pointed to being possible places where life may flourish.

However, despite the optimism of finding life on Titan there are some things to consider. Titan is extremely cold, and its atmosphere is thick enough to give an anti-greenhouse effect, cooling the planet. Chemical reactions as they take place on Earth would be completely different on Titan, with many elements taking different forms.

Looking at environments such as Mars and Titan as possible places for life to exist may seem far fetched. Quite how anything can survive at -290 degrees remains to be seen. However there are several examples of organisms thriving on Earth in extreme conditions. These creatures are called extremophiles and are found in some incredible places.

A good example of an extremophile is the Tardigrade, commonly referred to as the water bear. They are tiny creatures related to arthropods and are found all over the planet. They can be found 6000m above sea level high up in the Himalayas and at a depth of 4000m in the deep sea. They can be found in polar regions and round the equator. Incredibly they can survive temperatures close to absolute zero and as high as 151 degrees Centigrade as well as 1000 times more radiation than any other organism and for ten years without water. They have also been known to survive in a vacuum. It has also been found that they are able to withstand 6000 times atmospheric pressure, which is six times higher than the pressure found in the deepest trenches of the sea.

The fact that Tardigrades are so hardy points to the fact that life can flourish in the most incredible of environments. Given that these creatures evolved on Earth it doesn't seem to be hard to imagine that creatures with similar survivability have evolved to live on seemingly inhospitable planets. What is to say that the -290 degrees on Titan is too cold? We may even find that we're living in a uniquely hot environment that would kill most alien life.

When you sit back and look at the kinds of life on Earth and take a detailed look at the geography of extra-terrestrial moons and planets it seems hard to imagine that they're all lifeless. While researching for this article my opinion has shifted towards believing that should we find alien life that it will be far more similar to life found on Earth than we may think. Looking at the different evolutionary paths on Earth there are a lot of common features found in animals on our planet. Legs, eyes, mouths etc. Given that life must essentially function in much the same way as it does here in order to survive it isn't hard to imagine alien life being quite similar to life on Earth.

The question of whether we are alone or not in our solar system will be answered within our lifetime, and my belief has shifted from a positive yes to an unsure maybe. After learning of how hardy life on our planet can be and what kind of environments are out there, I do think that we will eventually find life on other worlds.
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